Spin on disposable or throwaway filters have been employed in numerous applications including hydraulic systems and engine lubrication systems. Such filters commonly include a thin gauge metal can or housing and a heavy stamped steel cover plate closing one end of the can. A central threaded hole is provided in the cover plate for securing the filter onto a threaded stud of a mounting base. The central opening and a plurality of surrounding openings in the cover direct fluid flow into and out of the filter. An annular seal is suitably connected to the cover radially outside of the plurality of holes and is compressed against a mounting surface of the mounting base to seal between the filter and mounting base when the filter is screwed onto the threaded study.
The outer shell or can of the filter is a pressure vessel which can be subjected to fluid pressure as high as 3450 kPa (500 psi) in some hydraulic systems. Because the seal is disposed radially outside of the plurality of holes, a rather large imbalance of forces is generated within the filter, resulting in large forces being exerted against the bottom of the can. For example, a force of about 1000 kg can be exerted against the bottom of the can of an 8 to 12 cm diameter filter subjected to typical system pressures. This sometimes causes the cover plate to flex sufficiently to unload the seal, permitting fluid to leak past the seal. In extreme cases, the flexure of the cover plate as the hydraulic pressures in the system go up and down causes a fatigue failure in the cover plate.
One solution to this problem is disclosed in U.S. Pat. No. 4,369,113 wherein the top plate is made excessively thick to accommodate the high imbalance of forces. However, making the top plate thicker adds to the cost and requires a special rolled lock seam to lock the cover plate to the can.
Another problem frequently encountered with the spin on fluid filters is that they are usually located in very confined locations, sometimes surrounded by other components such that visual installation of the filter is impossible. This makes the currently available disposable filter very difficult to install and remove. The person installing the filter must get the female threads in the cover plate of the filter exactly aligned with the threads on the threaded stud or the filter will cross thread. Once the threaded connection is initially made, several complete revolutions of the filter are required to bring the seal into contact with the mounting base. Then a very difficult last 1/2 to 3/4 turn is necessary to compress the seal while it slides along the mating surface of the mounting plate. In many cases, this must be done by wrist action only since a strap wrench can dent the can. Removal is just as difficult as the person tries to maneuver a strap wrench in a confined area. This is aggravated somewhat by the seal tending to adhere to the mounting base over a prolonged period, thereby requiring extra torque to break the seal loose.
The present invention is directed to overcoming one or more of the problems as set forth above.